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Encyclopedia > Celestial sphere
The celestial sphere is divided by the celestial equator.
The celestial sphere is divided by the celestial equator.

In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of "gigantic radius", concentric and coaxial with the Earth. All objects in the sky can be thought of as lying upon the sphere. Projected, from their corresponding geographic equivalents, are the celestial equator and the celestial poles. The celestial sphere projection is a very practical tool for positional astronomy. Image File history File links Celestial_Sphere. ... Image File history File links Celestial_Sphere. ... The celestial equator is a great circle on the imaginary celestial sphere, which could be constructed by inflating the Earths equator until it intersects with said sphere. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Table of geography, hydrography, and navigation, from the 1728 Cyclopaedia. ... Imagination is, in general, the power or process of producing mental images and ideas. ... A sphere rotating around its axis. ... A sphere (< Greek σφαίρα) is a perfectly symmetrical geometrical object. ... In classical geometry, a radius of a circle or sphere is any line segment from its center to its boundary. ... Concentric objects share the same center or origin. ... coaxial cable In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional analog of concentric. Coaxial cable, for example, has a conducting wire in the center and a second conducting layer running all the way around the exterior circumference, under the insulation. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... A typical daytime sky. ... Physical map of the Earth (Medium) (Large 2 MB) Geography is the scientific study of the locational and spatial variation in both physical and human phenomena on Earth. ... The celestial equator is a great circle on the imaginary celestial sphere, which could be constructed by inflating the Earths equator until it intersects with said sphere. ... The two celestial poles are the imaginary points where the Earths spin axis intersects the imaginary rotating sphere of gigantic radius, called the celestial sphere. ... Positional astronomy is the study of the positions of celestial objects. ...


The celestial sphere can be used geocentrically and topocentrically. The former means that it is centred around an imaginary observer in the centre of the Earth, and no parallax effects need to be taken into account. In the latter case it is centred around an observer on the surface of the Earth and then horizontal parallax cannot always be ignored; especially not for the Moon. The geocentric model (in Greek: geo = earth and centron = centre) of the universe is a paradigm which places the Earth at its center. ... This article or section does not cite its references or sources. ...


In the Aristotelic and Ptolemaic models, the celestial sphere was imagined as a physical reality rather than a geometrical projection (see heavenly sphere). Aristotle (Greek: Aristotélēs) (384 BC – March 7, 322 BC) was an ancient Greek philosopher, a student of Plato and teacher of Alexander the Great. ... Ptolemy, one of Alexander the Greats generals, was appointed satrap of Egypt after Alexanders death in 323 BC. In 305 BC he declared himself King Ptolemy I, later known as Soter (saviour). ... This drawing from an Icelandic manuscript dated around 1750 shows the Earth surrounded by the eight classical spheres. ...


The celestial sphere is divided by projecting the equator into space. This divides the sphere into the north celestial hemisphere and the south celestial hemisphere. Likewise, one can locate the Celestial Tropic of Cancer, Celestial Tropic of Capricorn, North Celestial Pole, and South Celestial Pole. The directions toward various objects in the sky can be quantified by constructing a celestial coordinate system. The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ...


As the Earth rotates from west to east around its axis once every 23 hours 56 minutes, the celestial sphere and all objects on it appears to rotate from east to west around the celestial poles in the same time. This is the diurnal motion. Therefore stars will rise in the east, culminate on the north-south line (meridian) and set in the west, (unless a star is circumpolar). Next night a particular star will rise again, but with our normal clocks running a 24 hour 0 minutes cycle, it will do so 4 minutes earlier. The following night that is already 8 minutes. And so forth every night (or day) again. A compass rose with west highlighted This article refers to the cardinal direction; for other uses see West (disambiguation). ... The Experimental Advanced Superconducting Tokamak (EAST, internally called HT-7U) is a project being undertaken to construct an experimental superconducting tokamak magnetic fusion energy reactor in Hefei, the capital city of Anhui Province, in eastern China. ... The Experimental Advanced Superconducting Tokamak (EAST, internally called HT-7U) is a project being undertaken to construct an experimental superconducting tokamak magnetic fusion energy reactor in Hefei, the capital city of Anhui Province, in eastern China. ... A compass rose with west highlighted This article refers to the cardinal direction; for other uses see West (disambiguation). ... The two celestial poles are the imaginary points where the Earths spin axis intersects the imaginary rotating sphere of gigantic radius, called the celestial sphere. ... Diurnal motion is an astronomical term referring to the apparent daily motion of stars in orbit around the Earth, caused by the Earths rotation around its axis. ... Meridian is: Meridian (astronomy): an imaginary circle perpendicular to the horizon. ... Circumpolar stars are those stars which are located near the celestial poles of the celestial sphere, i. ...


The reason for this apparent misadjustment of our clocks is that the Sun is not standing still on the celestial sphere, as the stars do, but moves about 1° per day eastwards over a great circle known as the ecliptic (which is 360° or a full circle in one year, the annual motion of the Sun). As an angle of 1° corresponds to 4 minutes in time (360° = 24 hours), we need therefore 4 extra minutes of diurnal motion to see the Sun back on (for example) the meridian again, making the duration of one rotation just 24 hours exactly (on the average, ignoring small seasonal variations, see equation of time) For the Brisbane bus routes known collectively as the Great Circle Line (598 & 599), see the following list of Brisbane Transport routes A great circle on a sphere A great circle is a circle on the surface of a sphere that has the same diameter as the sphere, dividing the... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... During the course of the year, the time as read from a sundial can run ahead of clock time by as much as 16 min 33 s (around October 31–November 1) or fall behind by as much as 14 min 6 s (around February 11–12). ...


Normal clocks therefore indicate solar time. Astronomers studying the movements of stars may want to have clocks indicating sidereal time, going around once in 23h56m (solar time units). Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ...


A celestial sphere can also refer to a physical model of the celestial sphere. Also known as a star globe, this sort of celestial sphere will indicate which constellations are visible at a given time and place.


See also

Medieval representation of a spherical Earth - with compartments representing earth, air, and water (c. ... This drawing from an Icelandic manuscript dated around 1750 shows the Earth surrounded by the eight classical spheres. ... Armillary sphere An armillary sphere (also known as spherical astrolabe) is a model of the celestial sphere, invented by Eratosthenes in 255 BC. Its name comes from the Latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking the poles and representing the equator, the... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ... Setting Circles are used on telescopes to find astronomical objects in the sky by their coordinates as listed in a star chart or ephemeris using the celestial coordinate system. ... The celestial horizon, also called the rational horizon, is a great circle parallel to the horizon, the center of which is the center of the Earth. ... An equinox is one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. ... The geocentric model (in Greek: geo = earth and centron = centre) of the universe is a paradigm which places the Earth at its center. ... Prograde motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called direct motion, especially in astrology. ... This article or section needs a complete rewrite for the reasons listed on the talk page. ... 360-degree panorama of the night sky with constellations superimposed. ...

External links

  • SkyandTelescope.com SkyChart
  • Monthly skymaps for every location on Earth

 
 

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